New to creating ASF add-ons? This is where to go: Creating a new add-on.
Where is everything? This is how it is organized:
ASF version independent information, recommendations, guidelines, tutorials, tips & tricks
For that, please browse the articles at the wiki.
Discussions and questions about ASF plugin development in general
These are conducted in the gitter chat room 
ASF add-on documentation, examples and tools
These are stored here, in this documentation and the files of this repository. For each ASF major version, the previous version gets its own branch.
The original "Extending Schema Form"-article is located here.
News, information and news relevant for ASF add-on-development
These are posted as issues for this project. Follow them to get the neccessary information.
(not sure if that works well, though, we'll see)